Counter-Strike. Half-Life. Team-Fortress. These were all among Valve's first generation of games. Built on a lean, innovative engine with world-class gameplay as their paramount goal, they were praised by critics as games that revitalized or even invented their genres.

Assume the role of Gordon Freeman in his debuton the last day he ever showed up for work as just an ordinary scientist. Or don a bullet proof vest and defeat 99 explosive terrorist plots in a single day. Or play as one of nine uniquely skilled mercenaries in their team's quest to defeat... another team who looks just like them. And when you're done with all that, dive into the wealth of add-on content and other titles in the series. All in all, eleven games that changed the world (and one that didn't). With over 14 million units sold, this group of titles is densely packed with gaming value and long-lasting fun.